Polyester film for metal sheet laminating

Abstract

A film to be laminated onto a metal plate and molded, which includes a first copolyester including ethylene-2,6-naphthalene dicarboxylate as a main recurring unit or a blend of the first copolyester and a second copolyester including terephthalate as a main recurring unit. Both the first copolyester and the blend contain diethylene glycol in an amount of 0.05 to 8 mol %. This film has a water extraction of 0.5 mg/inch 2 or less and a center line surface roughness (Ra) of 4 to 30 nm.

What is claimed is: 
     
       1. A biaxially oriented polyester film to be laminated onto a metal plate and molded: (A) which comprises a copolyester comprising (a) 2,6-naphthalenedicarboxylic acid in an amount of 80 to 100 mol % and either an aromatic dicarboxylic acid other than 2,6-naphthalenedicarboxylic acid or a combination of the aromatic dicarboxylic acid other than 2,6-naphthalenedicarboxylic acid and an aliphatic dicarboxylic acid in an amount of 20 to 0 mol % based on the total dicarboxylic acid components, and (b) ethylene glycol in an amount of 72 to 99.95 mol %, diethylene glycol in an amount of 0.05 to 8 mol %, and a glycol other than ethylene glycol and diethylene glycol in an amount of 0 to 20 mol % based on the total diol components, and having (c) a melting point of 198 to 268° C.;   (B) which has an extraction of 0.5 mg/inch 2  (0.0775 mg/cm 2 ) or less when subjected to an extraction treatment in ion exchange water at 120° C. for 2 hours; and   (C) which has a center line surface roughness (Ra) of the film surface in the range of 4 to 30 nm.   
     
     
       2. The polyester film of claim 1, wherein the dicarboxylic acid components of the copolyester comprises 80 to 100 mol % of 2,6-naphthalenedicarboxylic acid and 20 to 0 mol % of an aromatic dicarboxylic acid. 
     
     
       3. The polyester film of claim 1, wherein the diol components of the copolyester comprises 82 to 99.95 mol % of ethylene glycol and 0.05 to 8 mol % of diethylene glycol. 
     
     
       4. The polyester film of claim 1, wherein diethylene glycol is present in an amount of 0.1 to 5 mol % of the total of all diol components of the copolyester. 
     
     
       5. The polyester film of claim 1, wherein the copolyester contains germanium atoms derived from a polymerization catalyst in an amount of 40 to 200 ppm. 
     
     
       6. The polyester film of claim 1, wherein the copolyester has an intrinsic viscosity (measured in o-chlorophenol at 35° C.) in the range of 0.45 to 0.80 dl/g. 
     
     
       7. The polyester film of claim 1, which has an extraction of 0.3 mg/inch 2  (0.0465 mg/cm 2 ) or less. 
     
     
       8. The polyester film of claim 1, which has an Ra of 5 to 20 nm. 
     
     
       9. The polyester film of claim 1, which has a thickness of 6 to 75 μm. 
     
     
       10. The polyester film of claim 1, which contains fine particles, having an average particle diameter of 0.01 to 2 μm and a particle diameter ratio (long diameter/short diameter) of 1.0 to 1.2, in an amount of 0.01 to 1 wt %. 
     
     
       11. A biaxially oriented polyester film to be laminated onto a metal plate and molded: (A) which comprises a blend of a first copolyester comprising (a) 2,6-naphthalenedicarboxylic acid in an amount of 80 to 100 mol % and a dicarboxylic acid other than 2,6-naphthalenedicarboxylic acid in an amount of 20 to 0 mol % based on the total dicarboxylic acid components, and (b) ethylene glycol in an amount of 72 to 99.95 mol % and a glycol other than ethylene glycol in an amount of 0.05 to 28 mol % based on the total diol components, and having (c) a melting point of 198 to 268° C., and the second copolyester comprising (a') terephthalic acid in an amount of 90 to 100 mol % and a dicarboxylic acid other than terephthalic acid in an amount of 10 to 0 mol % based on the total dicarboxylic acid components, and (b') ethylene glycol in an amount of 90 to 99.95 mol % and a glycol other than diethylene glycol in an amount of 0.05 to 10 mol % based on the total diol components, and having (c') a melting point of 230 to 255° C., the content of diethylene glycol being 0.05 to 8 mol % based on the total mole number of the diol components of the first copolyester and the second copolyester;   (B) which has an extraction of 0.5 mg/inch 2  (0.0775 mg/cm 2 ) or less when subjected to an extraction treatment in ion exchange water at 120° C. for 2 hours; and   (C) which has a center line surface roughness (Ra) of the film surface in the range 4 to 30 nm.   
     
     
       12. The polyester film of claim 11, wherein the blend contains the first copolyester in an amount of 70 wt % or more based on the total weight of the first copolyester and the second copolyester. 
     
     
       13. The polyester film of claim 11, wherein the blend contains the first copolyester in an amount of 75 to 95 wt % and the second copolyester in an amount of 5 to 25 wt % based on the total weight of the first copolyester and the second copolyester. 
     
     
       14. The polyester film of claim 11, wherein the dicarboxylic acid components constituting the first copolyester comprises 80 to 100 mol % of 2,6-naphthalenedicarboxylic acid and 20 to 0 mol % of an aromatic dicarboxylic acid. 
     
     
       15. The polyester film of claim 11, wherein the diol components constituting the first copolyester comprises 82 to 99.95 mol % of ethylene glycol and 0.05 to 8 mol % of diethylene glycol. 
     
     
       16. The polyester film of claim 11, wherein the first copolyester contains germanium atoms derived from a polymerization catalyst in an amount of 40 to 200 ppm. 
     
     
       17. The polyester film of claim 11, wherein the intrinsic viscosity (measured in o-chlorophenol at 35° C.) of the first copolyester is in the range of 0.45 to 0.80 dl/g. 
     
     
       18. The polyester film of claim 11, wherein the first copolyester contains fine particles, having an average particle diameter of 0.01 to 2 μm and a particle diameter ratio (long diameter/short diameter) of 1.0 to 1.2, in an amount of 0.01 to 1 wt %. 
     
     
       19. The polyester film of claim 11, wherein the diol components of the second copolyester contain diethylene glycol in an amount of 0.05 to 8 mol % as a glycol other than ethylene glycol. 
     
     
       20. The polyester film of claim 11, wherein the second copolyester contains germanium atoms derived from a polymerization catalyst in an amount of 40 to 200 ppm. 
     
     
       21. The polyester film of claim 11, wherein the intrinsic viscosity (measured in o-chlorophenol at 35° C.) of the second copolyester is in the range of 0.50 to 0.80 dl/g. 
     
     
       22. The polyester film of claim 11, wherein the blend contains diethylene glycol in an amount of 0.1 to 5 mol %. 
     
     
       23. The polyester film of claim 11, which has an extraction of 0.3 mg/inch 2  (0.0465 mg/cm 2 ) or less. 
     
     
       24. The polyester film of claim 11, which has an Ra of 5 to 20 nm. 
     
     
       25. The polyester film of claim 11, which has a thickness of 6 to 75 μm.